Friday, January 25, 2013

New paper finds China was warmer than the present 1100 & 1700 years ago

A forthcoming paper in Climate of the Past reconstructs temperatures from 5 locations in China and finds no statistically significant change in temperature between the beginning of the record 2000 years ago to the end of the record in the year 2000. The paper shows the Medieval Warming Period about 1100 years ago and the Roman Warming Period ~1800 years ago were both warmer than the present.

Q. Ge, Z. Hao, J. Zheng, and X. ShaoInstitute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A Datun Road, Chaoyang District, Beijing 100101, ChinaAbstract. In this paper, we use principal components and partial least squares regression analysis to reconstruct a composite profile of temperature variations in China, and the associated uncertainties, at a decadal resolution over the past 2000 yr. Our aim is to contribute a new temperature time series to the paleoclimatic strand of the Asia2K working group, which is part of the PAGES (Past Global Changes) project. The reconstruction was developed using proxy temperature data, with relatively high confidence levels, from five locations across China, and an observed temperature dataset provided by Chinese Meteorological Administration covering the decades from the 1870s to the 1990s. Relative to the 1870s–1990s climatology, our two reconstructions both show three warm intervals during the 270s–390s, 1080s–1210s, and after the 1920s; temperatures in the 260s–400s, 560s–730s and 970s–1250s were comparable with those of the Present Warm Period. Temperature variations over China are typically in phase with those of the Northern Hemisphere (NH) after 1100, a period which covers the Medieval Climate Anomaly, Little Ice Age, and Present Warm Period. The recent rapid warming trend that developed between the 1840s and the 1930s occurred at a rate of 0.91° C/100 yr [but has since flatlined]. The temperature difference between the cold spell (−0.74° C in the 1650s) during the Little Ice Age, and the warm peak of the Present Warm Period (0.08° C in the 1990s) is 0.82° C at a centennial time scale.